Bearing arrangement

ABSTRACT

The invention relates to a bearing arrangement of a shaft ( 2 ), with which an annular bearing sleeve ( 4 ) is applied onto the shaft ( 2 ), wherein the shaft ( 2 ) at least in the axial region in which the bearing sleeve ( 4 ) is arranged, comprises a profiling extending parallel to its longitudinal axis (X), into which profiling a corresponding engagement element ( 12 ) on the inner periphery of the bearing element ( 4 ) engages with a positive fit, wherein at least one engagement element ( 12 ) extends in the direction of the longitudinal axis (X) of the shaft ( 2 ) only over a part of the length of the bearing sleeve ( 4 ).

The invention relates to a bearing arrangement of a shaft, in particular to a radial bearing arrangement.

A sliding bearing for a machine shaft, in this example, the rotor shaft of a pump assembly is known for example from 0 771 957 B1. With this sliding bearing, a bearing bush is applied onto the actual shaft.

With such bearing arrangements, the bearing bush is manufactured of a suitable bearing material, for example bronze or ceramic, whilst the rotor shaft is usually a conventional steel component. In order to permit a torque transmission from the rotor shaft onto the bearing bush, and to centre the bearing bush, it is known to profiling the shaft and to design corresponding profilings in the bearing bush, which engage with the shaft with a positive fit.

Bearing bushes of ceramic, have the advantage that they are very wear-resistant, ceramic however reacts very sensitively to tensile stresses. The problem is the fact that the coefficients of thermal expansion of the shaft which is manufactured of steel, and of the ceramic bearing bush are very different, which leads to undesirable tensile stresses in the ceramic and thus finally to damage of the ceramic bearing bush, on heating.

With regard to this problem, it is the object of the invention to provide an improved bearing arrangement of a shaft, in particular of a rotor shaft, with which the stresses occurring in a bearing bush or bearing sleeve are reduced.

This object is achieved by a bearing arrangement of a shaft with the features specified in claim 1. Preferred embodiments result from the dependent claims, the subsequent description as well as the attached figures.

The bearing arrangement according to the invention is particularly preferably suitable as a radial mounting for a rotor shaft, for example the rotor shaft of a pump assembly. The bearing arrangement comprises an annular bearing sleeve of a suitable bearing material, for example ceramic. This bearing sleeve is applied onto the shaft so that the bearing sleeve is arranged concentrically to the rotation axis of the shaft. The shaft, at least in the axial region, in which the bearing sleeve is arranged, is provided with a profiling for the transmission of torque and for centring the bearing sleeve on the shaft. This profiling extends parallel to the longitudinal axis of the shaft, so that it is possible to push the bearing sleeve onto the shaft along the profiling in the axial direction. The bearing sleeve comprises at least one complementary engagement element on the inner periphery. Particularly preferably, the inner periphery of the bearing sleeve is profiled complementarily to the outer periphery of the shaft. In this manner, the bearing sleeve by way of its engagement element, may engage with a positive fit with the profiling of the shaft, in order to effect the peripheral fastening and centring of the bearing sleeve on the shaft.

According to the invention, the engagement element is now designed on the inner periphery of the bearing sleeve, in a manner such that it extends in the direction of the longitudinal axis of the shaft only over a part of the length of the bearings leave. In this manner the stresses which act on the bearing sleeve from the outside may be reduced in the regions of the bearing sleeve, in which no engagement element is formed. These are in particular the outer regions of the bearing sleeve, in which the bearing sleeve comes to bear on adjacent components for the axial fixation of the bearing sleeve on the shaft. In particular therefore, no forces from the adjacent components may act directly on the engagement elements, so that these may not be damaged.

Preferably therefore, the at least one engagement element is distanced to the axial ends of the bearing sleeve in the direction of the longitudinal axis. I.e. no engagement elements are formed at the regions of the bearing sleeve which are adjacent to the axial end-faces or end-edges, so that in particular stresses occurring in these regions in the inside of the bearing sleeve may be reduced or eliminated. These regions are particularly sensitive, since these usually come to bear on steel muffs or steel sleeves which fix the bearing sleeve on the shaft in the axial direction, and bear on the axial end-faces of the bearing sleeve.

The regions of the bearing sleeve adjacent to the axial ends of the bearing sleeve are those regions in which the greatest stresses and/or deformations occur given the effect of external forces, in particular radial forces. By way of the arrangement of the engagement elements according to the invention, one succeeds in no engagement elements being formed in these regions, so that these in these regions may not become damaged. In particular, the danger of fractures on account of the notch effect in the transition to the engagement elements is reduced in these regions.

Further preferably, the at least one engagement element extends in the direction of the longitudinal axis over less than 50% of the length of the bearing sleeve. Thus that region of the bearing sleeve, which is engaged with the profiling of the shaft with a positive fit via the engagement elements, is reduced, so that the regions of the bearing sleeve which are subjected to the forces transmitted by the connection of the shaft, are also minimised.

Further preferably, the at least one engagement element is centred in the direction of the longitudinal axis with respect to the middle of the bearing sleeve. I.e. the one engagement element or the several engagement elements are distanced equally far from the two axial face ends of the bearing sleeve. In this manner, a symmetric construction of the bearing sleeve is achieved, with which the occurring stresses may be reduced in the same manner at both axial end-sides of the bearing sleeve.

Particularly preferably, several engagement elements are arranged on the inner periphery of the bearing sleeve, wherein the engagement elements are preferably distributed uniformly over the inner periphery. In this manner, the engagement elements are suitable in particular for centring the bearing sleeve on the shaft, and permit a uniform introduction of force or transmission of force from the shaft to the bearing sleeve.

Particularly preferably, the profilings of the shaft, at least the one engagement element, are designed as profilings, in particular wedge profilings, which correspond with one another. Such a wedge profiling permits a good centring of the bearing sleeve on the shaft.

According to a further preferred embodiment of the invention, the profiling of the shaft may be designed in the shape of a polygonal cross section of the shaft, and the at least one engagement element preferably defines a corresponding, polygonal inner cross section of the bearing sleeve. The complementary or fitting design of the inner cross section of the bearing sleeve to the outer cross section of the shaft permits an arrangement of the bearing sleeve on the shaft which is free of play in the radial direction, so that the bearing sleeve may be centred on the shaft by way of the profiling.

As specified above, the bearing sleeve is particularly preferably manufactured of ceramic. Ceramic is a particularly wear-resistant bearing material, which ensures a long service life of the bearing arrangement.

As already mentioned above, the bearing sleeve preferably for the axial fixation, bears with at least one axial end on a retaining muff or retaining sleeve which is applied onto the shaft. The retaining sleeve is fixed on the shaft in the axial direction and thus retains the bearing sleeve in the axial direction. Thereby, the bearing sleeve and the retaining sleeve bear on one another with their axial end-sides. The retaining sleeve may be supported on the shaft in the axial direction via a spring element, so that an extension on account of heating may be compensated in the axial direction, and despite this, the bearing sleeve may be held in the axial direction in a secure manner.

Since the bearing sleeve and the retaining sleeve are preferably manufactured of different materials, it results that the bearing sleeve and the retaining sleeve have different coefficients of thermal expansion. As described, the bearing sleeve is preferably manufactured of ceramic, whilst the retaining sleeve is preferably manufactured of steel. These different coefficients of thermal expansion lead to the fact that radial forces are transmitted from the retaining sleeve onto the bearing sleeve in the bearing region, which lead to stresses in the material of the bearing sleeve. In order to reduce the stresses precisely in these bearing regions, in which the bearing sleeve is in contact with the retaining sleeves, it is preferable to design the engagement elements on the inner periphery of the bearing sleeve in the manner described above. According to the invention, the engagement elements are distanced or set back from the axial ends of the bearing sleeve in the axial direction to such an extent, that they just do not come into contact with the retaining sleeves. In this manner, no external forces are transmitted onto the engagement elements in the radial direction by the retaining sleeves, so that here, no undesired stresses in the engagement elements or the profiling for centring the bearing sleeve on the shaft are created. In this manner the danger of damage to the bearing sleeve, in particular its engagement elements or profiling, on account of external forces is reduced.

The at least one retaining sleeve thereby is preferably designed such that at least at one axial end, i.e. that axial end with which it comes to bear on the bearing sleeve, it has a larger wall thickness than in its axial middle region. This permits an adequately large bearing surface to be ensured for the bearing on the bearing sleeve, at the axial end with a greater wall thickness. Simultaneously, a greater elasticity or spring effect of the retaining sleeve is achieved in the remaining regions of the retaining sleeve which have a lower wall thickness. Thus size changes occurring on heating may be accommodated by the retaining sleeve itself, due to its elasticity or spring effect. By way of this, the radial forces transmitted onto the bearing sleeve and which may occur on account of metal expansion on heating, are reduced.

Preferably, the retaining sleeve at its two axial ends has a greater wall thickness than in its axial middle region lying therebetween. In this manner, the axial ends which are provided for bearing on further components, are provided with bearing surfaces which are as large as possible. The middle region lying therebetween is designed more thinly or in a thinned manner, in order in this region to achieve the desired elasticity or spring effect. The retaining sleeve with an axial end bears on the bearing sleeve. With its opposite axial end, it bears on a securing element, for example a spring ring or securing ring, via which the retaining sleeve is supported on the shaft in the axial direction.

Further preferably, the retaining sleeve at least at one axial end has a radially inwardly or radially outwardly directed peripheral collar. Thus a greater wall thickness, or axial end-faces which are wider in the axial direction arise, which form the bearing surfaces, with which the retaining sleeve bears on the bearing sleeve or a securing element.

The retaining sleeve is preferably manufactured of metal, for example steel or however titanium. The design with titanium has the advantage that the expansion on heating may be reduced, since titanium has a lower coefficient of thermal expansion than steel. The difference in the size change between a ceramic bearing sleeve and the retaining sleeve on heating is reduced by way of this, by which means also the occurring forces and stresses in the components may be reduced.

The invention is hereinafter described by way of example and by way of the attached figures. In these there are shown in:

FIG. 1 in a schematic sectioned view, the basic construction of a bearing arrangement, from which the present invention proceeds,

FIG. 2 a schematic perspective view of a bearing sleeve according to the invention,

FIGS. 3 a-3 c schematic sectioned views of a retaining sleeve in three different embodiments,

FIGS. 4 a-4 c sectioned views of three further embodiments of a retaining sleeve,

FIG. 5 a a perspective view of a bearing sleeve with retaining sleeves arranged therein,

FIG. 5 b a plan view of the arrangement according to FIGS. 5 a and

FIGS. 6 a-6 d four different possible shaft profilings.

FIG. 1 schematically shows a bearing arrangement of a shaft, as is known from the state of the art and from which the present invention proceeds. With this bearing arrangement, a ceramic bearing sleeve 4 is arranged on the shaft 2. The bearing sleeve 4 surrounds the shaft 2 in an annular manner and is aligned or centred concentrically to its longitudinal axis X. For this, the bearing sleeve 4 is engaged with the shaft 2 with a positive fit via a profiling which is not shown in detail here. The bearing sleeve 4 in the axial direction is fixed on the shaft 2 via two retaining sleeves 6 which are supported on the shaft 2 in the axial direction, for example on securing rings (not shown). Thereby, at least one of the retaining sleeves 6 may be supported in the axial direction on the shaft 2 via a spring element, in order with temperature changes, to be able to compensate length changes of the retaining sleeves 6 and, as the case may be, of the bearing sleeve 4, which result therefrom. As is shown schematically in FIG. 1, the bearing sleeve 4 with its axial end-side 8, 10 bears in each case on a retaining sleeve 6, for the axial fixation. The axial end-regions of the bearing sleeve 4 which bear on the retaining sleeves 6, are subjected to particular stresses on account of the different coefficients of thermal expansion between the bearing sleeve 4 and the retaining sleeve 6, and are therefore particularly prone to wear. The retaining sleeves 6 are usually manufactured of steel or a different suitable material.

FIG. 2 shows a schematic embodiment of a bearing sleeve according to the invention. This bearing sleeve 4 comprises engagement elements 12 on its inner periphery. These engagement elements 12 are designed in a wedge-like manner in this example. What is essential is that they are designed complementarily to a profiling on the shaft 2, in order to be able to come into engagement with this with a positive fit, in order to centre the bearing sleeve 4 on the shaft 2 and to permit a torque transmission between the shaft 2 and the bearing sleeve 4. The engagement elements 12 are designed such that they have a constant cross section in the direction of the longitudinal axis X, so that it is possible to displace the bearing sleeve 4 in the axial direction in a complementary profiling on the shaft 2. What is essential is that the engagement elements 12 do not extend over the complete axial length in the direction of the longitudinal axis X of the bearing sleeve 4. In the shown example, they are only formed in the middle region in the axial direction, so that the axial ends of the engagement elements 12 are distanced to the end-sides 8 and 10 of the bearing sleeve 4. In this manner, it is ensured that no radial forces may be transmitted from the adjacent retaining sleeves 6 onto the engagement elements 12. One thus prevents the radial forces transmitted by the retaining sleeves 6 from causing undesired stresses in the engagement elements 12, which could lead to them getting damaged.

The preferred design of the retaining sleeves 6 is described in more detail by way of the FIGS. 3 and 4. The retaining sleeves shown in the FIGS. 3 a to 3 c and 4 a to 4 c are all designed such that they have no constant wall thickness over their axial length in the direction of the longitudinal axis X. Thus the retaining sleeves according to FIGS. 3 a to 3 c are in each case designed in a thickened manner in the radial direction at their axial ends 14, 16. The wall thickness is designed in a thinned or slighter manner in the middle region lying therebetween. In the embodiment according to FIG. 3 a, this is achieved by way of the wall of the retaining sleeve 6 being radially thickened to the outside at the axial ends 14 and 16, i.e. having a peripheral radially outwardly directed projection or shoulder. With the embodiment according to FIG. 3 b, the thickening at the two axial ends 14 and 16 extends radially to the outside as well as radially inwards. With the embodiment according to FIG. 3 c, the thickening of the peripheral wall of the retaining sleeve 6 is only designed by way of radially inwardly directed thickenings or projections at the axial ends 14 and 16. By way of the thickenings at the axial ends 14 and 16, bearing surfaces which are increased in size at the end side are created, with which bearings surfaces the retaining sleeve comes to bear for example on the axial end-sides 8, 10 of the bearing sleeve 4. Thus the retaining sleeve 6 at the axial ends 14 and 16 may have a wall thickness which corresponds to conventional retaining sleeves. The thinned-out middle region 18 effects an increased elasticity or spring effect of the retaining sleeve 6, which permits a compensation of the material expansion on heating. In this manner, with this retaining sleeve, the radial extension at the axial end-sides 14 and 16 and thus the radial forces transmitted there onto the abutting bearing sleeve 4 are reduced.

The embodiments according to FIGS. 4 a to 4 c correspond basically to the embodiments as have been explained by way of FIGS. 3 a to 3 c, with the difference that with the embodiments according to FIG. 4, only the one axial end 16 has the described thickenings. I.e. the axial ends 14 with regard to their wall thickness correspond to the middle region 18. Only with the embodiment example according to FIG. 4 b is there a radially inwardly directed thickening or a radially inwardly directed collar also at the axial end 14. There however, no radially outwardly directed collar is provided, as is the case at the axial end 16.

It is to be understood that all retaining sleeves 6 according to FIGS. 3 and 4 may comprise engagement elements or have a profiling in their inside, which is not shown here, and serves for coming into positive fit engagement with a corresponding profiling on the outer periphery of the shaft 2.

FIG. 5 shows the arrangement of a bearing sleeve 4 with two retaining sleeves 6 bearing thereon, according to the preceding description. Thereby, one may recognise that a first retaining sleeve 6 with its axial end 16 bears on the axial end-side 8 of the bearing sleeve 4, whilst a second bearing sleeve 6 with its axial end 14 bears on the opposite end-side 10 of the bearing sleeve 4. I.e. the bearing sleeve 4 is clamped between the two retaining sleeves 6 in the axial direction X.

FIG. 6 shows various profilings of the outer periphery of the shaft, wherein it is to be understood that the engagement elements or profilings on the inner periphery of the bearing sleeve 4 as well as of the retaining sleeves 6 are always formed in a complementary manner, so that they may come into positive-fit engagement with the shaft 2. With regard to the profiling according to FIG. 6 a, projections and grooves are formed extending in the longitudinal direction in an alternating manner in the shaft surface. With regard to the shaft according to FIG. 6 d, the shaft has a hexagonal cross section. The shaft 2 according to FIG. 6 c has a triangular cross section with convex side surfaces. The cross section of the shaft 2 according to FIG. 6 d comprises two grooves which are situated at diametrically opposite peripheral sides and which extend parallel to the longitudinal axis X, and into which engagement elements 12 on the inner periphery of the bearing sleeve 4 as well as corresponding engagement elements at the inner periphery of the retaining sleeve may engage.

It is basically to be understood that the profiling of the shaft may be designed in many different manners, wherein then the corresponding engagement elements formed on the inner periphery of the bearing sleeve 4 as well as the retaining sleeves 6 are designed in a complementary manner.

LIST OF REFERENCE NUMERALS

-   2—shaft -   4—bearing sleeve -   6—retaining sleeve -   8, 10—axial end-sides -   12—engagement elements -   14, 16—axial ends -   18—middle region -   X—longitudinal axis 

1. A bearing arrangement of a shaft (2), with which an annular bearing sleeve (4) is applied onto the shaft (2), wherein the shaft (2) at least in the axial region in which the bearing sleeve (4) is arranged, comprises a profiling extending parallel to its longitudinal axis (X), into which profiling at least one corresponding engagement element (12) on the inner periphery of the bearing element (4) engages with a positive fit, characterised in that the at least one engagement element (12) extends in the direction of the longitudinal axis (X) of the shaft (2) only over a part of the length of the bearing sleeve (4).
 2. A bearing arrangement according to claim 1, characterised in that the at least one engagement element (12) is distanced to the axial ends (8, 10) of the bearing sleeve (4) in the direction of the longitudinal axis (X).
 3. A bearing arrangement according to claim 1 or 2, characterised in that the at least one engagement element (12) extends in the direction of the longitudinal axis (X) over less than 50% of the length of the bearing sleeve (4).
 4. A bearing arrangement according to one of the preceding claims, characterised in that the at least one engagement element (12) is centred in the direction of the longitudinal axis (X) with respect to the middle of the bearing sleeve (4).
 5. A bearing arrangement according to one of the preceding claims, characterised in that several engagement elements (12) are arranged on the inner periphery of the bearing sleeve (4), wherein the engagement elements (12) are preferably uniformly distributed over the inner periphery.
 6. A bearing arrangement according to one of the preceding claims, characterised in that the profiling of the shaft (2) and the at least one engagement element (12) are designed as wedge profilings corresponding with one another.
 7. A bearing arrangement according to one of the claims 1 to 5, characterised in that the profiling of the shaft (2) is designed in the form of a polygonal cross section of the shaft (2), and the at least one engagement element (12) preferably defines a corresponding polygonal inner cross section of the bearing sleeve (4).
 8. A bearing arrangement according to one of the preceding claims, characterised in that the bearing sleeve (4) is manufactured of ceramic.
 9. A bearing arrangement according to one of the preceding claims, characterised in that the bearing sleeve (4) for axial fixation, bears with at least one axial end (8, 10) on a retaining sleeve (6) applied onto the shaft (2).
 10. A bearing arrangement according to claim 9, with which both axial ends (8, 10) of the bearing sleeve (4) bear in each case on a retaining sleeve (6) arranged on the shaft (2).
 11. A bearing arrangement according to claims 9 and 10, characterised in that the retaining sleeve (6) at least at one axial end (8, 10) has a greater wall thickness than in its axial middle region (18).
 12. A bearing arrangement according to claim 11, characterised in that the retaining sleeve (6) at its two axial ends (14, 16) has a greater wall thickness than in its axial middle region (18) lying therebetween.
 13. A bearing arrangement according to claim 11 or 12, characterised in that the retaining sleeve (6) at least at one axial end (14, 16) comprises a radially inwardly and/or radially outwardly directed, peripheral collar.
 14. A bearing arrangement according to one of the claims 9 to 13, characterised in that the retaining sleeve (6) is manufactured of metal, preferably steel or titanium. 